From type/Allomorph

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method uc(Allomorph:D:)

Calls Str.uc on the invocant's Str value.

From type/Cool

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sub uc(Str(Cool))
method uc()

Coerces the invocant (or in sub form, its argument) to Str, and returns it case-folded to upper case (capital letters).

say "Abc".uc;       # OUTPUT: «ABC␤»

From type/Str

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multi sub    uc(Str:D  --> Str:D)
multi method uc(Str:D: --> Str:D)

Returns an uppercase version of the string.